Laminated glasses are forms of safety glasses because few glass fragments are scattered even if they are broken into fragments by impact from the outside. The laminated glasses are widely used in windowpanes of, for example, motor vehicles such as automobiles, aircrafts, and buildings. Examples of the laminated glasses include laminated glasses having at least a pair of glasses integrated through an interlayer film for a laminated glass made of, for example, a polyvinyl acetal resin such as a polyvinyl butyral resin plasticized with a liquid plasticizer.
In recent years, entirely thin laminated glasses have been developed to achieve light weight and low cost. The disadvantages of these entirely thin laminated glasses are their low heat and sound insulation. Specifically, when these laminated glasses are used in, for example, windshields of vehicles, they problematically provide insufficient sound insulation against sounds around 2,000 to 5,000 Hz such as wind noise and sound of moving wiper, which have been conventionally cut out without difficulty.
In order to overcome these disadvantages, Patent Document 1 discloses an interlayer film for a sound insulating laminated glass having a sound insulation layer containing a large amount of a plasticizer sandwiched between covering layers containing a common amount of a plasticizer, as shown in FIG. 10. In this structure, the sound insulation layer provides high sound insulation, and the covering layers prevent the large amount of the plasticizer in the sound insulation layer from bleeding out. Therefore, the interlayer film for a sound insulating laminated glass provides high sound insulation as well as prevents the plasticizer from bleeding out.
However, laminated glasses incorporating the interlayer film for a sound insulating laminated glass disclosed in Patent Document 1 disadvantageously fail to sufficiently cut out sounds at specific wavelengths in a low temperature range and a high temperature range although they provide excellent sound insulation in a normal temperature range. For example, the service temperature of vehicles is as wide as −30 to 70° C. Interlayer films for a laminated glass which provide excellent sound insulation in a wide temperature range have been demanded.
The laminated glasses incorporating the interlayer film for a sound insulating laminated glass disclosed in Patent Document 1 have peaks of the loss factor in a normal temperature range and a high temperature range, which means that they provide excellent vibration damping performance. However, these laminated glasses may have an insufficient loss factor in a high temperature range. Sounds include airborne sounds such as noise of vehicles and alarm whistle, and structure-borne sounds such as sound produced by vibration of engines of vehicles. The disadvantage of these vibration damping laminated glasses is their insufficient vibration damping performance against structure-borne sounds in a high temperature range.